In order to implement governmental exhaust gas emission standards, provision is made among other things to reduce nitrogen dioxides NOx with the aid of a urea-water solution (HWL) via a catalytic converter in the exhaust gas tract. In so doing, the urea-water solution in the exhaust gas is converted into ammonia, which is deposited in the catalytic converter and reduces the NOx amounts. This method is denoted as selective catalytic reduction (SCR). The quantity of urea-water solution to be metered is ascertained in a separate metering strategy and is metered independent of boundary conditions by associated hydraulics and an electrical system.
The publication DE 10 2005 041 660 A1 relates to a method for introducing a reagent material into the exhaust gas region of an internal combustion engine and a device for implementing the method. According to said method, the reagent material, which is subjected to a reagent pressure, is metered by a reagent metering device as a function of a reagent signal. Furthermore, the pressure difference is ascertained between the reagent pressure and the exhaust gas pressure. The reagent signal is subsequently manipulated as a function of the pressure difference. With this method, the pressure difference can be taken into account and be used for correcting the reagent signal so that an under- or overmetering of the reagent material can be avoided.